Sunlight accelerates skin aging and even causes skin cancer, with these undesired effects being caused not only by UV-B radiation, but primarily by the UV-A radiation with wavelengths in the region of about 320 to 400 nm, which directly tans the skin.
It is already known from Swiss Patent 484 695 that the symmetrical tris-(2,4-dihydroxyphenyl)-1,3,5-triazines are very efficient UV-A/B light screening agents for the protection of textiles. A substantial disadvantage is, however, the extremely poor solubility of this class of compounds in practically all solvents, which does not permit them to be used, e.g., for cosmetic applications.
o-Hydroxyphenyl-s-triazines, which absorb UV light, are described in U.S. Pat. No. 3,896,125, but they are insoluble or soluble only with difficulty in non-polar polymers such as polyethylene, polypropylene or polyester resins.
Further, 2-hydroxyphenyl-s-triazines having a silicon-containing residue in in the 4-position of the 2-hydroxyphenyl group for the light stabilization of organic polymers are known from EP-A1-502821. In dimensionally stable articles produced from polymers stabilized therewith, the UV absorber contained in the outer layers of the article prevents the penetration of short-wave light which is especially harmful for polymers, i.e., primarily of UV-B radiation, into the interior of the article.
However, there exists the pressing need, especially for the producers of body care products, to make the hydroxyphenyl-s-triazine class of compound, having regard to its light screening action, also available for other purposes. Therefore, at least a good solubility in organic solvents, especially in cosmetic solvents, and a good photostability are required.